NEW YORK (Reuters Health) - Grape seed extract is marketed as a way to guard your heart health, but clinical trials so far suggest the supplement has small effects on blood pressure and heart rate, a new review finds.

Pooling the results from nine clinical trials, researchers found that on average grape seed extract shaved about 1.5 points from people's systolic blood pressure -- the top number in a blood pressure reading.

Still, diet changes -- like reducing sodium and getting plenty of fruit, vegetables, whole grains and lean protein -- have shown bigger effects on blood pressure numbers. So too have blood pressure medications, which some people may need to get their numbers under control.

Even more importantly, those steps may help prevent heart disease and stroke.

"Unlike diet and exercise," Coleman said, "there is no data with grape seed extract showing it will reduce patients' risk of heart attacks or strokes."

Among healthy seniors, the risk of stroke is generally low even with high blood pressure. Over 10 years, for instance, a 60-year-old man who doesn't smoke and doesn't have diabetes has a 3-to-10 percent chance of suffering a stroke, depending on his blood pressure.

For women, the risk is even lower. You can take a closer look at your own risk here: http://1.usa.gov/191PWr.

A number of studies have linked moderate wine intake with a lower risk of heart problems. That does not prove that wine deserves the credit, but researchers suspect there might be a heart benefit from the antioxidants found in wine. Antioxidants are substances that protect body cells from the damage that can eventually contribute to a range of diseases.

The rationale behind studying grape seed extract is that the supplement could offer those antioxidants in a more concentrated form -- without the alcohol.

For their review, which appears in the Journal of the American Dietetic Association, Coleman and his colleagues combined the results of nine clinical trials where people were randomly assigned to take grape seed extract or not.

Some trials included healthy people, while others focused on those with heart disease risk factors, like high blood pressure, high cholesterol or diabetes.

The studies lasted for anywhere from two weeks to six months, and the daily dose of grape seed extract ranged between 150 and 2,000 milligrams.

Overall, Coleman's team found, grape seed extract seemed to have a small effect on systolic blood pressure and heart rate, but no clear impact on cholesterol levels or diastolic blood pressure (the second number in a blood pressure reading).

Grape seed extract is considered generally safe, and a month's supply costs around $10. Some of the side effects that have been seen in studies include headache, dizziness, indigestion and a dry, itchy scalp.

But there is little known about the supplement's safety with long-term use (beyond a couple months). And it's not clear how it might interact with medications -- including drugs people may be taking to manage their heart risk factors.

Coleman said that, in theory, grape seed extract could increase the odds of bleeding. So it might be wise for people on aspirin or other drugs that "thin" the blood to avoid the supplement.

As far as effectiveness, Coleman suggested that people stick with the tried-and-true.

"People need to follow lifestyle and diet advice of their doctors," he said. "These measures will be far more effective that using grape seed extract."

SOURCE: http://bit.ly/qolGhz Journal of the American Dietetic Association, August 2011.